Power Estimation of an Active RFID Device

1 . A method comprising:

in a radio frequency identification (RFID) interrogator, interrogating a RFID device;

receiving an identification code, times and temperature data from the RFID device in response to the interrogation; and

estimating a remaining battery life of a battery in the RFID device.

2 . The method of claim 1 wherein estimating comprises:

determining a most recent temperature from the temperature data; and

predicting the remaining battery life from the most recent temperature.

3 . The method of claim 2 wherein predicting the remaining battery life comprises:

matching the most recent temperature to a temperature on a battery life expectancy curve; and

determining a battery life corresponding to the matched temperature on the battery life expectancy curve.

4 . The method of claim 3 wherein the battery life expectancy curve is plot of time and temperature.

5 . The method of claim 3 wherein the remaining battery life is the determined battery life.

6 . The method of claim 3 further comprising receiving a battery indicator from the RFID device.

7 . The method of claim 6 wherein the remaining battery life is calculated from the determined battery life and battery indicator.

8 . The method of claim 1 wherein estimating comprises:

determining an average temperature from the temperature data; and

predicting the remaining battery life from the average temperature.

9 . The method of claim 8 wherein predicting the remaining battery life comprises:

matching the average temperature to a temperature on a battery life expectancy curve; and

determining a battery life corresponding to the matched temperature on the battery life expectancy curve.

10 . The method of claim 9 wherein the battery life expectancy curve is plot of time and temperature.

11 . The method of claim 9 wherein the remaining battery life is the determined battery life.

12 . The method of claim 9 further comprising receiving a battery indicator from the RFID device.

13 . The method of claim 12 wherein the remaining battery life is calculated from the determined battery life and battery indicator.

14 . A method comprising:

in a radio frequency identification (RFID) device having a memory, temperature sensor and battery, periodically storing measured ambient temperatures; and

estimating a remaining battery life from the stored temperatures.

15 . The method of claim 14 wherein estimating comprises:

loading a most recent stored temperature; and

predicting the remaining battery life from the most recent stored temperature.

16 . The method of claim 15 wherein predicting comprises:

matching the most recent stored temperature to a temperature on a battery life expectancy curve; and

setting the remaining battery life to the battery life corresponding to the matched temperature.

17 . The method of claim 14 wherein estimating comprises:

determining an average temperature from the stored temperatures; and

setting the remaining battery life to a battery life corresponding to the average temperature on a battery life expectancy curve.

18 . A method comprising:

in a radio frequency identification (RFID) interrogator, interrogating a RFID device;

receiving an identification code, times, temperature data and battery voltage data from the RFID device in response to the interrogation; and

estimating a remaining battery charge in the RFID device.

19 . The method of claim 18 wherein estimating comprises:

setting the remaining battery charge to a battery charge corresponding to a last measured battery voltage on a battery charge life expectancy curve.

20 . The method of claim 18 wherein estimating comprises:

determining an average voltage from the received voltage data; and

setting the remaining battery charge to a battery charge corresponding to the average voltage on a battery charge life expectancy curve.

21 . A system comprising:

a radio frequency identification (RFID) device having a store of times and temperature data; and

a RFID interrogator programmed to interrogate the RFID, receive the times and temperature data, and estimate a remaining battery life of a battery in the RFID device from the times and temperature data.

22 . The system of claim 21 wherein estimating comprises:

determining a most recent temperature from the temperature data;

matching the most recent temperature to a temperature on a battery life expectancy curve; and

determining a battery life corresponding to the matched temperature on the battery life expectancy curve.

23 . The system of claim 21 wherein estimating comprises:

determining an average temperature from the temperature data;

matching the average temperature to a temperature on a battery life expectancy curve; and

determining a battery life corresponding to the matched temperature on the battery life expectancy curve.

24 . A system comprising:

a radio frequency identification (RFID) device having a store of times and temperature data; and

a RFID interrogator programmed to interrogate the RFID, receive the times and temperature data, and estimate a remaining battery voltage of a battery in the RFID device from the times and temperature data.

25 . The system of claim 24 wherein estimating comprises:

determining a most recent temperature from the temperature data;

matching the most recent temperature to a temperature on a battery voltage expectancy curve; and

determining a battery voltage corresponding to the matched temperature on the battery voltage expectancy curve.

26 . The system of claim 24 wherein estimating comprises:

determining an average temperature from the temperature data;

matching the average temperature to a temperature on a battery voltage expectancy curve; and

determining a battery voltage corresponding to the matched temperature on the battery voltage expectancy curve.